Researchers swabbed the entrances of the bat boxes for traces of genetic material to see who had been home, and found long-tailed bat DNA in a third of the boxes, according to the research published on Thursday in the New Zealand Journal of Zoology.

The bat box eDNA survey detailed in this study provides a non-intrusive method to confirm bats roosting in bat boxes within two years of box installation, said Fiona Davies, technical director of natural resources at AECOM NZ, an infrastructure consulting firm, part of the study.

Studies like these are essential to confirm the boxes are effective for bat conservation, Davies said, Xinhua news agency reported.

The results of the survey showed that the eDNA method was highly effective, and long-tailed bat DNA was detected at 34 percent of the boxes sampled, and she confirmed they were using the boxes.